Some progress, sort of.
I milled the wiper arm that attaches to the shaft into a 21mm hex and sacrificed the hand wheel because I didn't want make something to replace it.
So here's where I am.
Staring at it and waiting for a good idea...
Thanks KD. Some good stuff in that video!I may be going for a more red-neck solution than Lee.
I think for now I've settled on a solution.
I turned down the hand wheel to 20mm and decided against the nut/socket in favor of a 12mm to 20mm 66mm long flexible coupling (thanks Martin) that I'll just loosen with the set screw when I need to go manual.
The motor has three speeds and with the speed control I got, I'll be able to go from barely turning to faster than I'll ever use. So I don't know how often I'll want to go manual.
I also have stop/limit switches that I'm going to attach to the front slot somehow.
No progress until the coupler arrives from China.
I used a 12pt deep socket for my power feed. The motor has a 12t gear and a 3/4" socket fit perfectly. I took some 3/4" hex stock and pined it to the lead screw, cut the square drive from the socket, pressed a disc onto the middle of the socket and used that to manipulate the socket back and forth. I made a quick and dirty nylon forked lever to shift the socket. The gear on the motor has a small stub sticking out and I bored a hole in the one side of the hex stock to engage the stub to keep everything aligned.
For a power knee lift that is internal in my bridgeport knee I used a 24 volt pull solenoid to shift the gearbox of a 1/2 inch cordless drill. I didn't need the high speed side so I ground the gear teeth off on that side and that became neutral. A spring pulls it to the neutral side.
When the power is on for the motor to run the solenoid pulls the gearbox into gear and I can raise and lower the knee with a reversing switch. If I need to move the knee manually it can be done when the power supply is switched off.
It would take some doing but one of those little gearboxes could be installed between your motor and shaft.
I think that you will want to go to manual whenever you are positioning to a gnat's eyebrow. Sneaking up on that last half thousandth with a power feed will be tricky. If you overshoot, you will have to back up to remove the lash and have another go it. Changing from power feed to manual feed by loosening a set screw will get old really fast.
we use coupler identical to the one, you showed, we use them on 10 to 20 ft/lb, powered 90 degree actuators, we find unless they are keyed to the shaft, they will slip. The other option, for us, as the coupling is enclosed, we drill the coupling, and drive a roll pin into the coupling, through into the shaft. Leaving about 3/16"-1/4" of the roll pin sticking out, so it can be removed (we drill into the shaft, but not through the shaft).
The torque required to rotate the lead screw will be measured in oz.-in. The steppers on my Tormach mill are 500 oz.-in. and the coupling clamp is similar to the one you show and clamps onto a 1/2" shaft, no key. I have never had the coupling slip. You should be fine without drilling for a pin.
If it were me, I would prefer the coupling slip rather than running intro some obstruction that would cause more serious damage.
I chased this around for months on my mill.
Being able to disengage the power feed and complete the cut by hand is essential imo.
The best set up I could find was this one by Stefen Gotteswinter.
You can still make the connector even if you do not have a rotary table. Just mill a small plate with as many sides as you want teeth, and screw the connector to it.
I have other projects far more important to me than saving a few bucks on a power feed, so I dropped the money on one from Enco.
I had to fabricate an adaptor, I would post a photo but just discovered that Photobucket now charges $400.00/yr to embed images.
It is one of those items that gets used constantly, and every time I use it I am grateful I spent the money on it.